1. Field of the Invention
The present invention relates to a pneumatic tire, and in particular, relates to a pneumatic tire used for traveling on muddy roads.
2. Description of the Related Art
Four-wheel drive vehicles usually travel on not only dry asphalt roads, but also muddy roads. Therefore, tires for four-wheel drive vehicles are generally requested to have noise performance that offers silence for passengers on dry roads in addition to muddy road performance that offers high traction force on uneven ground such as loose muddy roads.
Japanese Unexamined Patent Application Publication No. 2012-218652 discloses a pneumatic tire that is expected to have a superior noise performance as well as muddy road performance.
FIG. 5 illustrates a developed view of the tread portion of the tire mentioned above. Referring to FIG. 5, the tread portion is provided with a pair of center main grooves “gc”, “gc”, and a pair of shoulder main grooves “gs”, “gs” arranged axially outwardly of the center main grooves “gc” to divide it into a center portion “ac”, a pair of middle portions “am”, and a pair of shoulder portions “as”. The shoulder portion “as” is provided with a plurality of shoulder lateral grooves “ys” to divide it into a plurality of shoulder blocks “bs”. The shoulder main groove “gs” extends in a trapezoid wave manner that includes a circumferentially extending axially outer part “gs1”, a circumferentially extending axially inner part “gs2” arranged axially inwardly of the axially outer part “gs1”, and an inclined part “gs3” connecting between the axially outer part “gs1” and the axially inner part “gs2”.
The shoulder lateral groove ys has an inclination angle in a range of from 5 to 20 degrees with respect to an axial direction of the tire, and is connected to the shoulder main groove gs at the inclined part gs3.
However, such a tire disclosed above has room for improving noise performance on dry roads.